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Wednesday, December 26, 2007

Energy saving - Repairing air leaks on compressed air lines

What is the results of air leaks on compressed air lines?

  • An air compressor works harder
  • An air compressor works longer

The above undesireable results make the compressor consumes more energy.

Eventhough air leaks is unavoidable, but with good house-keeping factory, the level of air leaks of 10% is acceptable. Most of the factories have air leaks far beyond that what mentioned.

Air leaks normally occur at the joints, flange connections, elbows, valves, filters, hoses, etc. as a result of thermal cycling and vibration.

How to detect air leaks?

  • Listen for hissing sound -- in some factories, even when in production process, we can still hear this sound if the leakage rate is high
  • Apply soap water at the location where the air leaks may present
  • Using an acoustic leak detector
  • Pressure drop test

Mechanical energy wasted caused by air leaks

The following equation expresses the actual mechanical energy wasted due to air leaks

where: 1 < n < 1.4 (isentropic) and 0.7 < hcomp < 0.9

From knowledge of fluid dynamics, we know that when line pressure P2 > 2 atm, the velocity of air at the leak site is equal to the local speed of sound.

Thus, the mass flow rate of air through a leak can be expressed as,

k = specific heat ratio = 1.4 for air
Cdischarge = 0.65 (approx.)

From the above equations, you can calculate yourself to see how the energy is wasted through air leaks if the leak site has 3 mm diameter and the line pressure Pline is 5 bar. You will see that a lot of money is wasted!!

Read more details how to save the energy

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